An electrostatic paint system consists of a paint booth or enclosure in which a coating such as paint powder is applied to parts, usually a conveyor is supplied for carrying parts into and out of the booth, and an electrostatic paint applying system. The paint applying system includes a powder spraying device which imparts a velocity to the paint powder articles which directs them toward the device to be painted, places an electrical charge on the powder particles, creates and electrical field between the device being painted and ground, and meters the powder. Electrically charged powder particles are attracted to and have an affinity for the grounded object to be painted since the grounded object assumes a polarity opposite that on the powder or spraying device. The charged powder particles are deflected from their original trajectory in the direction of the grounded object. An electrostatic adhesion system greatly increases powder transfer efficiency from the gun to the surface to be coated as compared to a non-electrostatic device.
The paint powder that does not adhere to the part is generally referred to as overspray. Overspray consists of powder that misses the part, rebounds from the part surface, and powder electrostatically deflected to other grounded surfaces such as spray booth metal components and article conveyors. Most overspray is entrained in the spray booth exhaust air.
To prevent oversprayed powder from polluting the workplace, and to provide for efficient powder recovery, articles are sprayed with powder while passing within the spray booth or housing. To recover the oversprayed powder, a filter system is employed through which the particulate entrained air from the spray booth is drawn. The filter system separates the powder form the air and the separated powder is then returned to the spray guns for reuse.
A problem common to all powder recovery systems is that of intermixing of differently colored powders between successive runs. In order to minimize this, it is known in the art to employ dedicated filter systems, such as cartridge cabinets, for each color to be run wherein each separate filter system is dedicated to recovery of only one particular color. That is, it is very difficult and time consuming to completely clean filter systems such as cartridge cabinets. Thus, dedicated filter systems are interchanged wherein a filter system dedicated to a given color is installed at the spray housing outlet when running that color, and replaced with another cabinet dedicated to the particular color to be run next. A primary concern in changing between successive colors is the prevention of intermixing of colors between successive runs. Even a small quantity of one color contaminating a second, different color will result in an undesirable speckling effect to sprayed articles or to a new batch of the second color whereby this batch must be replaced and scrapped.
In addition to helping prevent color intermixing, utilization of independent filter systems for each separate color provides significant time savings due to the elimination of the requirement that the filter system be completely cleaned between successive runs. Despite the time saved by interchanging filter systems, rather than cleaning the filters completely between runs of differing colors, considerable time is still required in blowing out the excess powder remaining in the spray housing, thoroughly scrubbing down the spray housing interior to completely remove any remaining overspray powder therefrom, and cleaning the hoses which supply the spray guns prior to running a subsequent color. It is required that this cleaning be thorough so as to prevent any contamination due to residual powder remaining in the spray booth and hose intermixing with the subsequent color run therethrough. Current designs utilize stainless steel spray booths since this material lends itself well to the repeated scrubbings required.
It is desirable to provide a powder recovery spray booth apparatus wherein the laborious task of cleaning the spray housing is eliminated while also providing improved means for assuring nc intermixing of separately colored powders.
One current design employs a plurality of adjacent rolls of plastic sheet wherein the sheets run along the interior side walls of the spray housing. The plastic sheet is unrolled and extended to cover the side walls of the spray housing. After running a first color, the sheets are advanced so that the powder tarnished portion of the plastic is moved out of the spray housing and a clean, unused portion of the plastic roll is brought into the housing. The theory is that by providing a clean portion of plastic to line the spray housing interior for each successive cartridge cabinet utilized, the aforementioned problems associated with color contamination are eliminated.
In practice, however, this design has been found undesirable in several respects. Powder has been found to accumulate in the gaps between adjacent plastic sheets which results in powder from one run remaining in the spray booth interior and intermixing with the differently colored powder passing therethrough in a subsequent run. Also, the plastic sheets do not cover the ceiling of the spray housing and powder accumulates thereat resulting in contamination of powders subsequently run through the spray housing interior. Furthermore, some operators find it cost prohibitive to continually resupply fresh plastic sheet for each successive run of differing color, and they scrub and clean plastic sheets for use with the second color rather than scrap the previously used plastic sheets. Therefore, there is a need for a spray booth apparatus which allows for successive runs of differing colors without the requirement of cleaning the spray housing interior between successive runs.